An image reading device having an auto document feeder (hereinafter, simply referred to as “ADF”) and a flat bed scanner (hereinafter, simply referred to as “FBS”) is known. The image reading device includes a close-contact line sensor such as a contact image sensor (CIS) reciprocating relative to a platen glass. A document placed on the platen glass is optically read by the line sensor while the line sensor moves along the platen glass. The document placed on a document bed of the ADF is optically read by the line sensor disposed at a predetermined reading position while the document is being conveyed along a conveying passage.
The above-mentioned line sensor is a reading device having a small focal distance and thus a small focused area. Accordingly, for example, in an image reading device using a contact image sensor (CIS) as a reading device, an adjustment of a relative distance between the CIS and a reading surface of a document is necessary to focus the CIS. For example, JP-A-2002-262032 discloses an image reading device that changes a height of the CIS to adjust a relative distance.
The image reading device disclosed in JP-A-2002-262032 includes a rail of which the longitudinal direction is a moving direction of the CIS. The CIS moves over the rail along the rail. A cross-section of the rail in a direction perpendicular to the longitudinal direction (axis direction) thereof is elliptical and the rail rotates around the axial direction by means of an operation of a lever, thereby serving as a disc cam. The CIS vertically moves with the rotation of the rail and thus gets close to or apart from a platen glass. That is, the relative distance between the CIS and the reading surface of a document on the platen glass is changed by means of the operation of the lever. JP-A-2002-262032 also discloses that a jack is disposed between the CIS and a supporting plate for mounting the CIS, and the CIS vertically moves by the use of the jack by operating a knob.
In the image reading device described in JP-A-2002-262032, a driving mechanism for rotationally driving the rail is required to adjust the relative distance between the reading surface of a document and the line sensor. When the driving mechanism is activated not manually but automatically, a driving source such as a motor is also required. Accordingly, the configuration is more complicated than that of an image reading device not having such a driving mechanism, which increases the cost for manufacturing the image reading device. Similar is caused in adjusting the relative distance between a document conveyed by an ADF and the line sensor.